The invention discloses a measuring device for measuring the mass of a weight, comprising: a main frame; a main beam supported on main frame; a balancing system loaded on one end of the main beam; a weighting system, loaded on the other end of the main beam; a weight transportation system capable of transporting and loading a standard weight or a test weight into the weighting system and capable of unloading and transporting them away from the weighting system; and a control system comprising an optical sensor mounted in the main frame, a laser displacement sensor mounted on the main beam, a monitor, and a control unit connected electrically to the optical sensor, the laser displacement sensor and the monitor. The control system is adapted to compare a main beam first displacement data obtained by the optical sensor and a main beam second displacement data obtained by the laser displacement sensor to accurately measure the actual displacement of the main beam.